1. Field of the Invention
This invention relates to tin and zinc catalysts containing nitrogen-metal bonds and to the use of the catalysts for the preparation of N-substituted acrylamides or methacrylamides by the catalytic reaction of an acrylate or methacrylate with an amine.
2. Prior Art
It is well known that certain .beta.-aminopropionamide compounds can be made by reacting dialkylamine compounds with an acrylic acid or ester compound, as described in John G. Erickson's article, "The Preparation and Stabilities of Some .beta.-Dialkylaminopropionamides," J. Am. Chem. Soc. 74, 6281-82 (1952). The reference discloses that N-N-dialkyl .beta.-dialkylaminopropionamides decompose, when heated at temperatures of about 125.degree.-215.degree. C., to the corresponding dialkylamines and N,N-dialkylacrylamides and that the ease of such decomposition decreases from the dibutylamine to the dimethylamine derivatives. Extensive polymerization of the substituted acrylamide products when certain of the .beta.-dialkylaminopropionamides are heated is also described.
It is known to react an alkali metal amide of a secondary alkyl amine with stannic chloride to provide the corresponding tin amide, wherein the amide is bonded directed to the tin, e.g.: EQU 4R.sub.2 Nli+SnCl.sub.4 Sn(NR.sub.2).sub.4 +4li cl
U.S. Pat. No. 2,451,436 to John G. Erickson teaches that N-alkylacrylamides can be prepared by subjecting an N-alkyl .beta.-alkylaminopropionamide, prepared by reacting 2 moles of an alkylamine or dialkylamine with an ester of acrylic or methacrylic acid, to elevated temperatures in the presence of a strong acid catalyst. The patent discloses that the acid catalytic process results in the formation of the salt of the aminoamide which splits when heated into the alkyl amine salt and the N-alkylated acrylamide, the latter distilling off during heating.
U.S. Pat. No. 2,529,838 to John G. Erickson teaches that certain N,N-dialkylacrylamides are produced by heating a dialkylamine containing at least 5 carbon atoms per alkyl group with a monomeric acrylic ester under superatmospheric pressure at temperatures between about 150.degree.-400.degree. C. The reference further teaches that dialkylamines containing fewer than 5 carbon atoms per alkyl group cannot be employed in the disclosed process.
Moreover, these prior art processes have been found to be disadvantageous for the preparation of certain N-(aminoalkyl)acrylamide compounds inasmuch as they typically produce tarry or gummy reaction mixtures from which it is difficult to separate a good yield of pure product. For example, the employment of the acid catalytic process described in U.S. Pat. No. 2,451,436 is reported to result in the production of alkylamino alkyl acrylamides in salt form which are not volatile and, hence, cannot be readily recovered by distillation separation procedures. Moreover, the process described in U.S. Pat. No. 2,529,838 requires very high temperatures and superatmospheric pressures wherein the reactions are of long duration.
In view of these disadvantages, the above-described processes have been considered inapplicable for the preparation of N-(tertiaryaminoalkyl)acrylamides and several alternative processes have been described. For example, U.S. Pat. No. 2,649,438 to Bruson, teaches that certain N-(tertiaryaminoalkyl)acrylamides can be prepared by reacting .beta.-propionlactone, ##STR1## with the desired tertiary amino diamine and distilling the reaction product under reduced pressure whereby dehydration readily occurs. The patent further teaches that other N-(tertiaryaminoalkyl)acrylamides can be obtained by reacting the appropriate acrylyl chloride with the desired tertiary amino diamine.
U.S. Pat. No. 3,652,671 to Barron describes a process for preparing N-(dialkylaminoalkyl)methacrylamides wherein the Michael adduct of methacrylic acid and a N,N-dialkylalkylenediamine; that is, the N-(dialkylaminoalkyl)-2-methyl-.beta.-alanine, is subjected to an elevated temperature of about 140.degree.-230.degree. C. which results in substantially complete rearrangement to the N-(dialkylaminoalkyl)methacrylamide product. This process has the disadvantage of being applicable only to the preparation of N-(dialkylaminoalkyl)methacrylamides which are obtained from methacrylic acid adducts. The patentee teaches that the use of corresponding adducts of acrylic acid in the described process gives poor results with side reactions predominating. The reaction mixtures produced by heating these adducts are stated to be largely by-products and tarry materials from which only small quantities of the desired acrylamide can be separated.
In view of the unavoidable secondary reactions at high temperatures, two-stage processes for the preparation of N-substituted acrylamides or methacrylamides have hitherto proved advantageous. In the process described in U.S. Pat. No. 3,878,247, one mole of an acrylate or methacrylate is reacted with 2 moles of an amine in the first reaction stage at a temperature below 200.degree. C. The Michael addition and aminolysis proceed concomitantly, so that the corresponding .beta.-aminopropionamide or isobutyramide is obtained as an intermediate product. In the second reaction stage the amine added to the double bond is removed at temperatures above 200.degree. C., the substituted acrylamide or methacrylamide being obtained.
In order to avoid undesirable Michael addition, the process described in U.S. Pat. No. 2,719,175 involves the reaction of esters of acrylic or methacrylic acid which amines at 300.degree.-550.degree. C. in the gaseous phase in the presence of solid catalysts such as vanadium-aluminum oxides with contact times of a few seconds to form the corresponding substituted acrylamides or methacrylamides. The high reaction temperature favors uncontrolled decomposition and polymerization reactions, so that yields of at most 50% are obtained.
U.S. Pat. No. 4,206,143 reveals that dialkyl stannic oxide catalysts, such as dibutyl stannic oxide, are effective for the preparation of N-substituted-acrylamides and -methacrylamides from the reaction of an alkyl ester of acrylic or methacrylic acid with an aliphatic, cycloaliphatic or aromatic amine, which is a primary or secondary amine. Similarly, a method whereby methacrylate or acrylate esters are treated with N,N-dialkyldiaminoalkanes in the presence of organotin compounds, such as dibutyldimethoxytin, to give (meth)acrylamides having tertiary amino groups is described in U.S. Pat. No. 4,321,411.
U.S. Pat. No. 4,228,102 discloses that certain N-substituted acrylamides may be made by reacting an ester with an amine with heating under pressure where the amine is present in an amount which is stoichiometrically deficient up to an amount which is in small stoichiometric excess with respect to the ester. However, the only example therein which is run under those conditions gave the poor yield of 32% to the amide. The other examples of that patent all employ an acidic catalyst to obtain a better yield.
It would be desirable to have a process for the production of N-substituted acrylamides in high yield which could be performed in one step which did not employ corrosive, acidic catalysts or excessive temperature and pressure conditions, which have been problems with the previously described methods.